1. Technical Field
This invention relates in general to integrated circuit (IC) dice and, in particular, to devices and methods for testing dice in IC modules.
2. State of the Art
Integrated circuit (IC) dice are typically tested before they are packaged to determine if they have any failing circuitry. In general, one of the first steps in testing a die is to initiate a test mode in the die by applying control signals to selected bond pads on the die referred to as test bond pads. As an example, most Dynamic Random Access Memory (DRAM) dice manufactured by the Assignee of this invention, Micron Technology, Inc. of Boise, Idaho, are tested in a test mode initiated, in part, by applying a logic "0" signal to their Output Enable (OE) bond pad.
As shown in FIG. 1, when multiple dice 10 are packaged together in an IC module 12, their test bond pads 14 (e.g., their OE bond pads) are often interconnected with their reference voltage bond pads 16 to the reference voltage V.sub.SS through module terminals 18 to ensure that a test mode cannot be accidentally initiated in an end user's system. While this works well to prevent accidental initiation of a test mode in dice in an IC module in the field, unfortunately it also prevents intentional testing of the dice by an IC manufacturer after they are packaged in the IC module.
One conventional solution to this problem, described in U.S. Pat. Nos. 5,278,839 and 4,519,078, is to eliminate the need to initiate a test mode in the manner described above by incorporating self test circuitry into dice. Because the self test circuitry is controlled through address and control bond pads that generally are not fixed to the reference voltage V.sub.SS or supply voltage V.sub.CC, a test mode can be initiated with the self test circuitry after the dice are packaged in an IC module. However, self test circuitry is a cumbersome and expensive solution that does not address the need for a solution that is easily incorporated into existing dice and IC modules.
Because it would be advantageous to have the flexibility to test dice after they are packaged in an IC module, there is a need in the art for an improved device and method for initiating and performing such testing.